Re: [RFC][PATCH 2/4] interruptible rwsem operations (i386, core)

[David Howells <dhowells@redhat.com>]

Dominik Brodowski <linux@dominikbrodowski.de> wrote:

> Add functions down_read_interruptible, and down_write_interruptible to rw
> semaphores. Implement these for i386.
> ...

> +static inline int
> +rwsem_down_interruptible_failed_common(struct rw_semaphore *sem,
> +			struct rwsem_waiter *waiter, signed long adjustment)
> +{
> ...

I wonder if you should check to see if there are any readers that can be woken
up if a sleeping writer is interrupted, but I can't think of a simple way to
do it.

> -struct rw_semaphore fastcall __sched *
> -rwsem_down_read_failed(struct rw_semaphore *sem)
> +void fastcall __sched rwsem_down_read_failed(struct rw_semaphore *sem)

Please don't.

> @@ -199,14 +253,33 @@ rwsem_down_read_failed(struct rw_semapho
>  				RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS);
>  
>  	rwsemtrace(sem, "Leaving rwsem_down_read_failed");
> -	return sem;

Ditto.

> -struct rw_semaphore fastcall __sched *
> -rwsem_down_write_failed(struct rw_semaphore *sem)
> +void fastcall __sched rwsem_down_write_failed(struct rw_semaphore *sem)

Ditto.

> @@ -216,10 +289,31 @@ rwsem_down_write_failed(struct rw_semaph
>  	rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS);
>  
>  	rwsemtrace(sem, "Leaving rwsem_down_write_failed");
> -	return sem;

Ditto.

> @@ -99,11 +103,12 @@ static inline void __down_read(struct rw
>  {
>  	__asm__ __volatile__(
>  		"# beginning down_read\n\t"
> -LOCK_PREFIX	"  incl      (%%eax)\n\t" /* adds 0x00000001, returns the old value */
> +LOCK_PREFIX	"  incl      %0\n\t" /* adds 0x00000001, returns the old value */

Ditto.

>  		"  js        2f\n\t" /* jump if we weren't granted the lock */
>  		"1:\n\t"
>  		LOCK_SECTION_START("")
>  		"2:\n\t"
> +		"  movl      %2,%%eax\n\t"

Splat.

>  		"  pushl     %%ecx\n\t"
>  		"  pushl     %%edx\n\t"
>  		"  call      rwsem_down_read_failed\n\t"

Splat.

> @@ -113,11 +118,41 @@ LOCK_PREFIX	"  incl      (%%eax)\n\t" /*
>  		LOCK_SECTION_END
>  		"# ending down_read\n\t"
>  		: "=m"(sem->count)
> -		: "a"(sem), "m"(sem->count)
> +		: "m"(sem->count), "m"(sem)
>  		: "memory", "cc");
>  }

You appear to be corrupting EAX.

> +static inline int __down_read_interruptible(struct rw_semaphore *sem)

Will corrupt EAX.

>  		"# beginning down_write\n\t"
> -LOCK_PREFIX	"  xadd      %%edx,(%%eax)\n\t" /* subtract 0x0000ffff, returns the old value */
> +LOCK_PREFIX	"  xadd      %%edx,%0\n\t" /* subtract 0x0000ffff, returns the old value */

Again, please don't. It's a lot more readable when it mentions EAX directly,
plus it's also independent of constraint reordering.

> +static inline int __down_write_interruptible(struct rw_semaphore *sem)

Will corrupt EAX and EDX.

David